1. Field of the Invention
The present invention relates to a method and system for manufacturing reformed hydrogen rich fuel by causing carbon-containing fuel to react with steam. This reformed fuel is preferably used as fuel for a boiler, gas turbine, gas engine, or fuel cell.
2. Description of the Related Art
In relation to the manufacture of reformed hydrogen rich fuel, a method and system using a steam reforming oven (heating type steam reforming oven) including a multi-tube reactor which causes a steam reforming reaction between carbon-containing fuel and steam are known. This method and system cause a partial oxidation reaction using a gas containing carbon-containing fuel and an appropriate amount of steam, and oxygen, oxygen rich air, or air.
The reaction temperature of a steam reforming reaction must be very high, from the viewpoint of chemical equilibrium of the reaction, in order to obtain a desired high conversion degree. In a conventional multi-tube reactor filled with a reforming catalyst, the tube wall and the flow of gas are parallel, so heat flow between the tube and catalyst and heat flow in the catalyst filling layer are not excellent. Therefore, the surface temperature of the tube wall must be held higher in order to maintain a necessary reaction temperature.
In addition, to improve the heat flow in the catalyst filling layer and lower the temperature of the tube wall, the tube diameter must be decreased to a certain degree. Also, since the steam reforming reaction is an endothermic reaction, a large quantity of heat must be transferred to a source gas at high temperatures. This requires a reaction tube made of a high-grade material having a large heat transfer area. So, these methods and systems are not economically advantageous.
On the other hand, U.S. Pat. No. 6,387,845 B1 discloses a carbon dioxide gas absorbent selected from the group consisting of lithium silicate, represented by formula LixSiyOz (wherein x, y, and z are integers satisfying x+4y−2z=0). U.S. Pat. No. 6,387,845 B1 also discloses a method of separating and collecting carbon dioxide gas in an exhausted gas by using this absorbent.
Jpn. Pat. Appln. KOKAI Publication No. 10-152302 discloses a reactor which produces a predominant gas and a by-product gas of carbon dioxide by a chemical reaction of a source gas, and a chemical reaction apparatus which is installed in this reactor and contains a compound which produces a carbonate by reacting with carbon dioxide. Jpn. Pat. Appln. KOKAI Publication No. 10-152302 describes that the production rate of the predominant gas can be raised by efficiently removing carbon dioxide from the reaction field.
Unfortunately, in this technology described in Jpn. Pat. Appln. KOKAI Publication No. 10-152302, a quantity of heat required for the steam reforming reaction cannot be easily transmitted to a reforming catalyst, and increasing the size of the apparatus is difficult, from the economical viewpoint. Also, the steam reforming catalyst must be separated from a carbon dioxide absorbent via a porous partition and filled in each zone. This makes assembly and maintenance of the apparatus itself difficult.
It is thus an object of the present invention to provide a method and system capable of obtaining a desired high conversion degree at relatively low temperatures in a steam reforming reaction, capable of obtaining reformed fuel having high hydrogen purity, and capable of making an apparatus necessary for steam reforming inexpensive. It is another object of the present invention to obtain a carbon dioxide-containing gas having a high carbon dioxide content in addition to the reformed fuel.